Products and apparatus fabricated by welding metal parts together are common. Equally common is the understanding that during welding, heat is transferred to the metal parts and can cause a degree of distortion in such parts. For many applications, such distortion is not critical, either because the final product does not require close dimensional tolerances or because such product will be clamped or otherwise integrated into a larger structure which forcibly removes the distortion.
On the other hand, there are applications for fabricated weldments which are much more demanding in terms of dimensional tolerances. That is, certain types of fabricated weldments require a high degree of precision in the final product ---- significant distortion and resulting misalignment simply cannot be tolerated.
An example of such an application involves fabricated end trucks for cranes. Overhead traveling cranes have parallel main girders supported at either end by a wheeled end truck. The trucks ride on elevated rails as the crane transports loads from one location to another. Similarly, the crane trolley rides back and forth on girder-mounted rails and is supported on such rails by end trucks.
Typically, each end truck has a pair of spaced-apart flanged wheels, one near either extremity of the truck. To avoid abnormal wear of rails and wheels alike, such wheels must be "lined up" with respect to the rail. Wheels that are angularly misaligned with respect to a rail are said to be "skewed."
To describe this phenomenon in more precise, geometry-like terms and with respect to a crane end truck, assume that each wheel has a "wheel plane," i.e., a plane through the wheel perpendicular to its axis of rotation and midway between its lateral sides. In order for the wheels to track straight and true along the rail, the wheel plane of each of the two wheels must be substantially vertical and coincident with one another and with the rail longitudinal centerline. A wheel that is skewed (and there may be one or two such wheels on a particular end truck) has a wheel plane that is vertical but laterally angularly oriented with respect to that of the other wheel and/or with respect to the rail centerline.
Another type of wheel misalignment, less of a potential problem than wheel skewing described above, involves wheels mounted with axes of rotation which are not parallel to the rail centerline. That is, a wheel (or both wheels) and its axis of rotation are tipped inward or outward. As used herein, misalignment of this type is said to involve a "tipped" wheel. And a tipped wheel has a wheel plane which is not vertical. While one or more tipped wheels can cause undue wear, this type of misalignment is significantly less serious than wheel misalignment by skewing.
An improved weldment fabrication method which overcomes the aforementioned problems would be an important advance in the art.